The present study was aimed to see the effect of surface treatment on nanocomposites with different fatty acids (stearic acid and oleic acid) having two different coupling agents (titanate and silane). Nanocomposites were prepared via melt mixing in Haake 90 twin screw extruder. The characterization of nanocomposites had been carried out using various advance analytical techniques such as dynamic mechanical analysis, thermogravimetric analysis, heat distortion temperature, melt flow index, and scanning electron microscopy. The strength and stiffness were also improved with the incorporation of maleic-anhydride grafted ethylene propylene rubber in PP/Nano-CaCO3 nanocomposites. The tensile, flexural, and impact strength properties of PP/MA-g-EPR/treated-CaCO3 and untreated nanocomposites were determined. These studies revealed that stearic acid treated nanofiller filled composites had better properties than those of untreated and oleic acid treated nanofiller filled composites. The SEM studies demonstrated that the dispersion and distribution of Nano-CaCO3 (nCaCO3) particles within the polypropylene matrix were dependent on the nature of surface treating agents. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012